Can a 3.5" HDD be enclosed in an external USB-C enclosure with USB-C Power Delivery [PD] and have a USB-C cable from the computer as the only power source to avoid a second power cable?
Does such a case exist?
Super User is a question and answer site for computer enthusiasts and power users. It only takes a minute to sign up.Sign up to join this community
Looking at some old 3.5" HDDs I have stacked in my basement I see that they require less than 1 amp on both the 5 volt and 12 volt DC input pins, most less than 1/2 an amp. This means they will take less than the 15 watts that many USB-C ports on many computers can supply, and many less than the 7.5 watts that is the minimum a USB-C port must provide to meet the USB-C spec.
A problem with this is that the ports on most computers will only supply 5 volts, and the drives will need 12 volts. It is possible to have a voltage boost circuit to create the 12 volt supply but that is an expensive circuit to build in the thin margins of consumer electronics. It is far less expensive to build a buck circuit to take a higher voltage to a lower voltage, and that's how some enclosures get the 3.3 volts that some drives use off a 5 volt supply from USB-C or USB-A.
It is unlikely such cases exist on the market. The profit margins are thin and the power budget is thin. The people making the cases must assume 5 volts at 1.5 amps from the USB-C port as that is the specified minimum for USB-C compliance. 3 amps from USB-C is common but not universal. 12 volts from USB-C was optional in USB-PD 1.0 but 5 years later became deprecated in favor of 9 volts and 15 volts when USB-PD 2.0 was published. USB-PD 1.0 was not very popular for some reason, it seems the people behind USB would rather everyone forgot it existed.
If we assume that the case for a 3.5" HDD must have room for 12 volts at 1 amp for the drive then that right there takes 12 watts. Then comes the 5 volt supply which might take 1/2 an amp, 2.5 watts. Then the interface board will need power. That's cutting it close even if the people engineering the case know that there will be 15 watts available.
The question did specify use of USB-PD for the drive enclosure power. USB-PD is only required if the client device is going to ask for more power than the 5 volts at 3 amps allowed with the USB 3.x spec. In most computers there will be a 12 volt supply but, again, supplying this out the USB-C port is not part of the current spec. It is allowed for backward compatibility to USB-PD 1.0 devices but, shall we say, "discouraged". Boosting that up to 15 volts is possible, then in the drive it can be bucked down to 12 volts and 5 volts easily enough. The USB-C ports on most computers that claim "high power" will be 15 watts (5 volts at 3 amps) or maybe 27 watts (9 volts at 3 amps). If they provide 12 volts then it's at most 27 watts, or 2.25 amps. Then after the 12 volts gets to the drive maybe there is more than 2 amps to work with, or maybe not because 2.25 amps is a maximum and not a minimum.
The thin power margins on USB-C under USB 3.x makes it difficult to power a 3.5" HDD. Requiring USB-PD for power means very few buyers as USB-PD output on computers is slim to none, and people willing to pay extra to not need an external power supply will also be slim to none. If such an enclosure exists then I'd be very surprised.
USB C PD 2.0 dropped mandatory 12V (and PD 1.0 is a paper only standard) and made that voltage optional. So our theoretical enclosure would only work with certain power supplies which is annoying and it's not possible for the end user to easily tell from the wattage alone. For eg. I have a non-spec compliant laptop which requires 12V 2.5A over USB C to charge and it's a major annoyance to figure out which 30W power banks can supply it. PD 3.0 introduced PPS which would be another source of 12V but again some chargers implement it and some don't.
Looking at How much power does a hard drive use? we can see some hard drives use above 20W when spinning up which means even if we tried to boost the voltage of the max 15W 5V supply, it wouldn't be enough always. While that is old, looking at more modern hard drives say 6-14TB WD Red Plus 1.75A-1.85A maximum is still there.
So you would have an enclosure which doesn't always work which would make customers unhappy, review scores low and support costs high. This is a no go.
Another solution would be to make the enclosure a full docking station: take 20V 5A, negotiate with the laptop for 65W max and use the remaining wattage by converting the 20V down to 12V. I speculate when I say the cost of this would probably make such a thing not alluring to consumers especially when compared to the really low cost separately powered HDD enclosures so no one bothered to make one.
You could, of course, use 15V and make the enclosure standalone but once you add a voltage converter circuit the relative added cost of another USB C PD controller is very low and the results would make more sense because if you are powering the enclosure and the laptop separately, what's the point of using USB C power for the enclosure...?
USB type is supposed to be able to supply 100w or 20v at 5amps.
It is physically possible to design a circuit to request the necessary power to provide all the power necessary to run a 3.5" hard drive.
1 amp at 5v is 5w and 1 amps at 12v is 12w. So the total is 17w. Now there will be a power loss in the conversion process, but if your USB type C port actually provides 100w there is a large margin of error.
However, the BIG problem is not every USB type C port is actually 100% compliant. Many don't offer the 100w option, but if yours does it is possible.
Now I don't know if anyone has actually done this or not.